Removing Cannabis Leaves to Maximize Light

A few days ago, a friend asked me when he should start removing leaves on his indoor medical cannabis plants. The tops of the plants were becoming crowded with big healthy leaves; and he was concerned about light penetrating to the lower branches. I was surprised by how many wrong and contradictory answers he had received from other fairly experienced growers. Hopefully I can clarify a few points and help dispel some of the misinformation floating about.

Try to think of leaves like solar panels. They are the plant’s only source of energy. The healthier the leaves, the more energy the plant has to grow and produce huge, resinous buds.

As the leaves on the plant begin to age, they eventually reach a point where photosynthesis peaks and begins to slow. At this point, the leaves are less efficient, and glucose productions declines. New leaves grow in to replace them as the primary solar panels, allowing more efficient photosynthesis to continue. The older, less efficient, leaves begin to work much like the root system, distributing their stored nutrients and plant sugars to wherever it is needed. When they have no more nutrients left to redistribute, these leaves will begin to yellow, and eventually fall from the plant.

This is particularly important to remember if you are experiencing root problems. Older leaves may be sacrificed to allow light to shine on fresh growth–but only if you have a healthy, robust root system. If your roots are not well established or are damaged, you may do more harm than good by removing the older leaves.

I should point out that most of the older leaves will be lower on the plant and therefor unlikely to shade much of the fresh growth. Any fresh growth lower on the plant is probably on shoots and in the shade of fresh foliage that is closer to the light. The principles of light and the inverse square law tell us that artificial light intensity quickly diminishes the further you get from the light source. So, you certainly do not want to sacrifice fresh leaves closer to the light for fresh leaves further away.

You can tell that leaves are beginning to give up their nutrients when they start to lose their dark green color. If these fading older leaves are blocking the light from new growth, feel free to remove them. By the time the leaves become pale green, or begin to yellow, they should be removed–even if they are not blocking younger foliage. Be sure not to remove leaves that have not yet reached their full size, unless they have been damaged by pests. Healthy leaves exposed to the light are facilitating photosynthesis. So your plants require them.

Outside, the Sun’s position in the sky changes through the day, providing light from a wide range of angles. Plants will follow the Sun and lower their leaves in the morning and evening to expose as much surface area as possible to the light. In grow rooms with stationary grow lights, the plants will only receive light from one static angle. This means that lower leaves are often shaded completely once new leaves grow in.

With stationary lighting, the only wavelengths that can penetrate dense leaves is from the far red end of the spectrum. This far red light does not assist photosynthesis, but triggers internal plant hormones called gibberellins. These gibberellins then cause the plants to stretch and create longer internodal spacing. The lower, shaded shoots usually do not amount to much, but may draw a tremendous amount of the plant’s energy stretching towards the light. For indoor gardens, use selective pruning to maximize yield and redirect plant energy to more productive zones.

Removing leaves is not the only method of decreasing shading and increasing light penetration. Using light movers, you can supply light at a variety of angles. This can reduce stretch, and light otherwise shaded leaves. Oscillating fans can be aimed to flutter leaves, allowing light to penetrate deeper into the canopy. Reflective material on the walls will also help to redirect wasted light at angles advantageous to lower leaves. For smaller grow rooms, plants can be set at different levels like stadium seating. In theory, this works great; but it is difficult to implement in larger grow rooms, and virtually impossible with many hydroponic systems.

The best answer for improving light penetration is simply to grow shorter marijuana plants. This is one reason that “See of Green” gardens yield so well. With taller plants, the majority of the bottom branches end up in shade. Even if light did penetrate the upper leaves, the lumens reaching the lower branches are so diminished that they yield poorly anyway.

What have you learned?

Do not remove leaves indiscriminately.

Do not remove young leaves unless heavily damaged by bugs or molds.

Do not sacrifice healthy leaves near the light for the sake of lower leaves.

Grow your plants short to keep all the branches as close to the lights source as possible

Use selective pruning to remove sucker shoots that use up valuable plant energy

One final thing to remember: when you remove leaves from your plants, be sure to remove them from the grow room. Piles of leaves in the corner, or in a garbage can, will likely begin to harbor pests or molds. The last thing you want is a waste basket full of botrytis spreading spores through your garden and ruining your harvest.

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I’m just your average Joe from a small town in the northern California hills. I’ve spent half my life growing marijuana and I’m still no expert. It’s been a bumpy but fun ride. Now it’s time to hang up my farmers hat. These days I’m chasing around the real experts with a laptop in one hand and a video camera in the other.

20 Comments »

Good well written piece Rambo, I’m amazed by the number of new and experienced growers who seem to think that removing the fan leaves will help the plant and confuse good pruning practices with “leafing”.

Its just easier to quote Robert Connell Clarke’s excellent Marijuana Botany on this one:

” Large leaves have a definite function in the growth and development of Cannabis. Large leaves serve as photosynthetic factories for the production of sugars and other necessary growth sub stances. They also create shade, but at the same time they are collecting valuable solar energy and producing foods that will be used during the floral development of the plant. Premature removal of leaves may cause stunting, because the potential for photosynthesis is reduced. As these leaves age and lose their ability to carry on photo synthesis they turn chlorotie (yellow) and fall to the ground. In humid areas care is taken to remove the yellow or brown leaves, because they might invite attack by fungus. During chlorosis the plant breaks down substances, such as chlorophylls, and translocates the molecular components to a new growing part of the plant, such as the flowers. Most Cannabis plants begin to lose their larger leaves when they enter the flowering stage, and this trend continues until senescence. It is more efficient for the plant to reuse the energy and various molecular components of existing chlorophyll than to synthesize new chlorophyll at the time of flowering. During flowering this energy is needed to form floral clusters and ripen seeds.”

Thank you! There is certainly plenty of myth and misinformation when it comes to growing marijuana.

Fox houseDecember 5, 2013 at 10:44 am -

In Jorge’s “bible” it says to lollipop for yield, in the photo it shows NAKED branches, with only the last flowers left… I was curious why they put that in the book, so don’t do that?

45YrTokerFebruary 24, 2012 at 3:46 pm -

Just one thing about those inefficient shoots that you’re cutting off. Last season, as I was removing them, I decided to clone one of the shoots. It was truly a pathetic looking scrawny took root in June. The mother was grown from FEMINIZED seed and sprouted in late March. I’ve been using fem seeds for 4 years with no hermies. Also know how to make fem seed and have 1 gal of 40% Gib just waiting. If anyone needs some I’ll make a much better price than you’ll see anywhere else-just let me know.

That single clone increased my harvest by 1/2 Lb. If you’re spending money on seed, like I do, then stop paying for 10 seeds. 3 are plenty, if you clone those weak lower shoots. I’ve had plants that had at least 15 good shoots I could have taken for clones. If you’re only growing for your stash, instead of 10 seeds of one variety, get single seeds of 10 different varieties. If you take just one clone from each plant, you’ll have 20 plants, 2 of each variety, and if you’re outdoors, you’ll likely get at least a pound @ plant. Think how much fun you’ll have tasting and smoking 2 Lbs of 10 varieties for the next 2 or 3 years!

Thanks for bringing that up. You are certainly correct about cloning the branches that are removed. I have successfully run motherless and seedless grow rooms for years on end. If you time things correctly, the branches you prune off can be the clones for the next cycle.

Van HappåFebruary 22, 2013 at 6:25 am -

Thänks!

This was very useful information and text was well written. Every grower should read this. =)

albertMay 9, 2013 at 10:45 am -

Im growing a plant from seed and my sun leaves are starting to sprout new starts now that is strange so im trying to indentify the strain?

One side of the plant broke or a leaf broke off? I’m not sure I understand. That’s why the forum is a better place for questions like this, you can post pictures and get better answers to you questions.http://www.marijuanagrowershq.com/forum/

S.B.September 2, 2013 at 2:10 pm -

I have tried and tried to tell my husband not to cut off the leaves, he gets down right MAD at me. Hopefuly reading this will chane his mind… Does removing the leaves chane the quality of the bud or just the size of the plant?

removing leaves effects the health of the plant. If a plant is unhealthy it will not produce quantity or quality.

Learning247October 22, 2013 at 3:55 pm -

@S.B.

Your husband is doing the right way, he will see an increase in his yields and it will NOT change the quality of the bud, as a matter of fact I won’t be surprised if it’s a bit more resinous. Defoliation should be done starting in Veg and then continued in flower after the initial 2-3 week stretch. I guarantee you will see more bud sites as soon as the plant starts to bud.

@Rambo

Have you ever tried the defoliation method? Because if you haven’t your article is not entirely correct and based on conjecture, because no one has done any extensive research on cannabis. There is more to this wonderful plant than meets the eye.

I have tried the defoliation method and I disagree with you, but thank you for sharing your thoughts.

first time growerJanuary 10, 2014 at 3:18 pm -

my plant just spouted and its getting talller but the leaves have not came out yet.what am i doing wrong?do i need more light?

SusanJanuary 11, 2014 at 7:50 am -

Rambo,

Can you tell me how to clone? I am growing medical cannabis in a small grow box using hydroponics.

kandyApril 11, 2014 at 2:53 pm -

Great learned ng article. I am on my second small harvest 3plants in flower.thank you for your hard earned information

ErvMay 31, 2014 at 8:05 pm -

@first time grower- put the light a little closer to stop stretch- cfl works wonders! Lol and @susan- you tube that bad boy!

Mansion RollersJune 10, 2014 at 8:53 am -

I defoliate and have seen an increase in yield and potency. I have a strategy to it, not just plucking all the fans. It works for me so I’m sticking to it. I have tried both ways with same strains. Defoliation has won every time. Different strokes for different folks. What works for me with short bushy indicas may not be good on a sativa.